Data analysis Quantitative analysis of the MR blood flow data will be performed on a Leonardo Workstation using Argus perfusion analysis software. Images were registered manually by adjusting the horizontal and vertical registration of each frame. The left and right ventricular blood pool and six myocardial regions will be analyzed to extract the linear slope during the initial signal increase as well as the starting and peak signal intensities. To extract the slope, base, and peak signals, a line was manually fitted to the upslope signal (typically 4-6 time points), and the base and peak positions of the upslope data were manually identified. Normalized slope (SlopeN) was calculated by division by the left ventricular blood pool slope, and the net signal gain (SG) determined by subtracting the initial from the peak signal intensity. The myocardial flow reserve index was calculated for each myocardial region as the ratio of the normalized hyperemic time-intensity slope to the normalized baseline time-intensity slope.